This invention pertains to an apparatus for improving the performance of Ceramic Metal Halide (CMH) lamps by replacing the current four-part electrode/leadwire assembly used in typical CMH lamps with a three-part electrode/leadwire assembly. More particularly, the invention relates to a uniquely configured electrode/leadwire assembly having a single continuous elongated shaft or mandrel which supports an electrode tip and a transition overwind component and eliminates a welded interconnection previously used in present assemblies to join together shank portions of dissimilar material that support molybdenum and tungsten portions of the lamp assembly together.
CMH lamps have become increasingly more popular due to their significant customer benefits. CMH lamps replace more traditional quartz arctubes found in arc discharge lamps with a ceramic arctube. CMH lamps provide better color uniformity and stability, as well as increased lumens per watt, relative to traditional arc discharge lamps. Because the ceramic arctube can operate at a higher temperature than a comparable quartz arctube and has a much lower rate of sodium loss, a CMH lamp is able to achieve the foregoing advantages.
In conventional CMH lamps, the electrode leads are manufactured and assembled from at least four distinct parts. The five part electrode/leadwire assembly, for example as used in 70 watt and 100 watt CMH lamps, includes an electrode tip (generally formed from tungsten), an overwind component (generally formed from molybdenum), an electrode mandrel, an overwind mandrel, and a niobium outer lead. The electrode mandrel and the overwind mandrel are welded together to form a shank. The two pieces of wire that comprise the shank are typically tungsten and molybdenum, with the latter having a larger diameter. Once the wires are welded together, the tungsten section of the mandrel supports the electrode tip and the molybdenum section supports the overwind component. Together, these components form the electrode/leadwire assembly. The niobium outer lead is also welded to the outer end of the molybdenum section of the shank.
Current CMH lamps are difficult to fabricate with precise alignment and stability between the tungsten electrode tip section and the molybdenum transition section. These difficulties are associated with the fact that the mandrel is presently constructed from two pieces of dissimilar materials, adding further complexity to the assembly. Because the two wires are so small, welding them together with precision is a difficult and arduous task resulting in low yields from the welding process, alignment problems, and decreased stability. As a consequence, CMH lamps encounter undesirable failures due to broken electrode tips caused when the weld breaks.
To date, the difficulties in manufacturing electrode/leadwire assemblies for ceramic metal halide lamps and the attendant problems associated therewith have not been resolved. The CMH lamps currently in existence lack the strength and stability to provide optimum performance. The prior art, which incorporates the four-part electrode/leadwire assembly, has not adequately remedied the shortcomings of present CMH lamps. Thus, a need exists to provide an electrode/leadwire assembly that is easier to manufacture and which provides increased strength and stability in operation.
A new and improved electrode/leadwire assembly for a ceramic metal halide lamp is provided having increased strength and stability.
In an exemplary embodiment of the invention, the apparatus employs an electrode/leadwire assembly having a single continuous mandrel, shank, or shaft supporting an electrode tip and an overwind component.
The CMH lamp preferably includes an envelope enclosing an interior chamber having elongated legs extending therefrom. Each leg houses an electrode/leadwire assembly. The shaft or mandrel of the electrode/leadwire assembly is constructed from a single, continuous, homogenous wire preferably formed from tungsten. The inner end of the mandrel supports an electrode tip also made from tungsten. In addition, a molybdenum overwind component is supported by the mandrel at a predetermined position spaced from the electrode tip. During manufacture of the electrode/leadwire assembly, the electrode tip and overwind component are attached to the mandrel through conventional winding and tacking techniques. Because the mandrel is formed from a single element, the present invention eliminates the welded arrangement. As a result, the electrode/leadwire assembly is stronger and more stable which prevents early lamp failure.
A principal advantage of the invention is provided by eliminating the weld in CMH electrode/leadwire assemblies, thereby reducing lamp shrinkage and increasing the leadwire""s stability.
Another advantage of the invention resides in the improved concentricity of the electrode tip, which reduces arctube wall corrosion, resulting in increased lamp life and better performance.
Still another advantage of the invention is a more consistent heat conduction from the electrode tip, thereby increasing lamp life by reducing tip burn back and reducing operating voltage rise.
Yet another advantage of the invention resides in the reduced cost to manufacture this less complex ceramic metal halide lamp.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.